1. Field of the Invention
The present invention relates to a method for quantitatively analyzing steer characteristics to acquire steering stability of vehicles/tires, and more particularly to a method for quantitatively analyzing steer characteristics, which divides the steer characteristics into understeer, oversteer, and power-off reaction characteristics, separately analyzes the understeer, oversteer, and power-off reaction characteristics, analyzes the understeer characteristic using a turning curvature and a turning velocity in association with a vehicle turning path, analyzes the oversteer characteristic using a slope of a nose angle and a nose-angle time rate in association with a vehicle attitude, analyzes the power-off reaction characteristic using a nose-angle slope, a nose-angle change rate, and a nose-angle change amount, and compares the above-mentioned characteristics with reference data obtained from a Quasi steady-state condition test during which a vehicle driving state is stable, such that it can quantitatively determine the steer characteristics upon receipt of the result of the comparison.
2. Description of the Related Art
A representative method for quantitatively analyzing understeer and oversteer characteristics of a vehicle using a reference data concept is described in U.S. Pat. No. 4,969,212 filed by Walter et al, entitled “QUANTITATIVE MEASUREMENT OF HANDLING CHARACTERISTICS OF TIRES AND/OR VEHICLE/TIRE COMBINATIONS”, which is incorporated herein by reference. The method of the U.S. Pat. No. 4,969,212 compares lateral acceleration and yaw rate generated during a vehicle running time with reference lateral acceleration and reference yaw rate, respectively, such that it quantitatively analyzes understeer and oversteer degrees.
A representative method for estimating performance of a tire using a steady-state turn test, a lift-off test, a transient state test, an emergency lane change test, and an emergency J-turn test is described in U.S. Pat. No. 6,580,980 filed by Gauthier et al, entitled “SYSTEM AND METHOD FOR TESTING DEFLATED TIRE HANDLING”, which is incorporated herein by reference. The method of U.S. Pat. No. 6,580,980 provides a method for quantitatively analyzing steering stability performance of a tire using both a subjective estimation method associated with individual test methods and an objective estimation method associated with measurement data.
The last performance estimation in a vehicle/tire design process is performed by subjective assessment of an expert driver. Particularly, many parts contained in a steering stability estimation process depend on the subjective assessment method, such that the subjective assessment result is reflected in all analysis methods. The above-mentioned methods of U.S. Pat. Nos. 4,969,212 and 6,580,980 indicate the subjective assessment result of an expert estimator using basic parameters associated with vehicle movement, for example, lateral acceleration, yaw rate, and vehicle velocity parameters. However, indeed, an expert estimator prefers to perform the subjective assessment using perceptual parameters corresponding to individual assessment parameters, instead of using the above-mentioned basic vehicle movement parameters. Therefore, the above-mentioned methods have difficulty in substantially reflecting the subjective assessment result of the expert estimator in the vehicle/tire design process.